Hydraulics
What are Hydraulics?
Hydraulic modeling contains data on the modeled water surface elevations of flooding throughout a floodplain - this same information contained in HEC-FDA Version 1 Water Surface Profiles.
What is the Purpose of Hydraulics?
Hydraulic modeling is used in HEC-FDA to identify the water surface elevation at each structure for at least 8 unique events. This information is used in calculating the stage-damage functions for each structure, after which the structure-level stage-damage functions are aggregated to stages at the index point which are defined by the combination of the input summary relationships. The hydraulics data can also be used to develop a graphical stage-exceedance probability functions.
Where Do I Get Hydraulics?
Hydraulic engineers will use HEC-RAS or some other hydraulic modeling software to develop the spatial data sets.
Working with Hydraulics in HEC-FDA
Hydraulics Overview
There are two options for importing hydraulic modeling into HEC-FDA:
- Grids (.tif), or
- Hierarchical data format (.hdf).
Hydraulic modeling can be exported from HEC-RAS in either format; hierarchical data format is the more convenient option.
The hierarchical data format export is described in HEC-RAS 2D User's Manual here. If the hydraulic modeling is steady state, one HDF will be imported. If the hydraulic modeling is unsteady state, all HDFs in the model-specific subdirectory will be imported. For example, if the existing condition model was run for 8 events, there should be those 8 HDFs in a dedicated folder and none else. Depth grids will not be handled by the software directly and are not advised for use with the stage-damage compute.
Gridded data is described in the HEC-RAS Mapper User's Manual here. Whether steady state or unsteady state, the gridded data must be organized in 8 subdirectories, one subdirectory with one .tif for each flood event, similar to how unsteady state modeling is organized.
| Hydraulic Data | Terrain | Impact Area Set | Index Point Set |
|---|---|---|---|
| Unsteady HDF | Required. | Required. | Optional. Only used for retrieving stage-frequency from hydraulics data set. |
| Steady HDF | Required. | Required. | Optional. Only used for retrieving stage-frequency from hydraulics data set. |
| Gridded Data | Optional. Can be used if elevation data is not present in inventory. | Required. | Optional. Only used for retrieving stage-frequency from hydraulics data set. |
Differences Between HEC-FDA Versions 1 and 2
Hydraulics data is used the same way in HEC-FDA Version 2 as it was in Version 1 - to calculate stage-damage functions. The main difference in the data used by the two versions is the format. The data consumed by Version 1 consisted of a table of data organized by river mile - a 1-dimensional view of the world. In Version 2, the data is represented within a geospatial data set. In Version 2, the hydraulics modeling does not contain flow information like in Version 1, so data on flow-frequency functions and stage-discharge functions must be obtained separately.
Steps to Import Hydraulics
- Right click on the desired import format under Hydraulics in the Study Tree and select Import
- Enter a name and a description.
- Browse for the location of the data sets. For steady and unsteady data, you'll select the folder that contains the HDFs for the modeled hydraulic events. For gridded data, a separate subfolder for each modeled hydraulic event should be included and contain the associated TIF files.
- Verify and correct the exceedance probabilities if needed
- Click Save. See below for completed import.
